package web

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strconv"
	"time"
)

type apiError struct {
	Error string `json:"error"`
}

func writeJSON(w http.ResponseWriter, code int, v interface{}) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(v)
}

func writeError(w http.ResponseWriter, code int, msg string) {
	writeJSON(w, code, apiError{Error: msg})
}

func methodAllowed(w http.ResponseWriter, r *http.Request, methods ...string) bool {
	for _, m := range methods {
		if r.Method == m {
			return true
		}
	}
	writeError(w, http.StatusMethodNotAllowed, "method not allowed")
	return false
}

func decodeBody(w http.ResponseWriter, r *http.Request, v interface{}) bool {
	r.Body = http.MaxBytesReader(w, r.Body, 4<<20) // 4 MiB is plenty for a rule file
	if err := json.NewDecoder(r.Body).Decode(v); err != nil {
		writeError(w, http.StatusBadRequest, "invalid request body: "+err.Error())
		return false
	}
	return true
}

// POST /api/v1/login
func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodPost) {
		return
	}
	var req struct {
		Password string `json:"password"`
	}
	if !decodeBody(w, r, &req) {
		return
	}
	token, expiry, err := s.auth.login(r.RemoteAddr, req.Password)
	if err != nil {
		code := http.StatusUnauthorized
		if errors.Is(err, errTooManyAttempts) {
			code = http.StatusTooManyRequests
		}
		writeError(w, code, err.Error())
		return
	}
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    token,
		Path:     "/",
		Expires:  expiry,
		HttpOnly: true,
		Secure:   s.TLS(),
		SameSite: http.SameSiteLaxMode,
	})
	writeJSON(w, http.StatusOK, map[string]interface{}{
		"token":     token,
		"expiresAt": expiry.UnixMilli(),
	})
}

// POST /api/v1/logout
func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodPost) {
		return
	}
	s.auth.logout(bearerToken(r))
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    "",
		Path:     "/",
		MaxAge:   -1,
		HttpOnly: true,
		Secure:   s.TLS(),
		SameSite: http.SameSiteLaxMode,
	})
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

// GET /api/v1/info
func (s *Server) handleInfo(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodGet) {
		return
	}
	var info Info
	if s.config.Info != nil {
		info = s.config.Info()
	}
	writeJSON(w, http.StatusOK, info)
}

// GET /api/v1/meta
func (s *Server) handleMeta(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodGet) {
		return
	}
	writeJSON(w, http.StatusOK, s.config.Meta)
}

// GET /api/v1/metrics
func (s *Server) handleMetrics(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodGet) {
		return
	}
	writeJSON(w, http.StatusOK, s.config.Hub.Metrics())
}

// GET /api/v1/events?limit=200
func (s *Server) handleEvents(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodGet) {
		return
	}
	limit := 200
	if v := r.URL.Query().Get("limit"); v != "" {
		if n, err := strconv.Atoi(v); err == nil && n > 0 {
			limit = n
		}
	}
	writeJSON(w, http.StatusOK, map[string]interface{}{
		"events": s.config.Hub.Events(limit),
	})
}

// GET /api/v1/live - server-sent events carrying live events and metrics.
func (s *Server) handleLive(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodGet) {
		return
	}
	flusher, ok := w.(http.Flusher)
	if !ok {
		writeError(w, http.StatusInternalServerError, "streaming unsupported")
		return
	}
	h := w.Header()
	h.Set("Content-Type", "text/event-stream")
	h.Set("Cache-Control", "no-cache")
	h.Set("Connection", "keep-alive")
	h.Set("X-Accel-Buffering", "no")
	w.WriteHeader(http.StatusOK)
	flusher.Flush()

	events, unsubscribe := s.config.Hub.Subscribe()
	defer unsubscribe()

	metricsTicker := time.NewTicker(2 * time.Second)
	defer metricsTicker.Stop()
	keepAlive := time.NewTicker(20 * time.Second)
	defer keepAlive.Stop()

	send := func(event string, v interface{}) bool {
		data, err := json.Marshal(v)
		if err != nil {
			return true
		}
		if _, err := fmt.Fprintf(w, "event: %s\ndata: %s\n\n", event, data); err != nil {
			return false
		}
		flusher.Flush()
		return true
	}

	if !send("metrics", s.config.Hub.Metrics()) {
		return
	}
	for {
		select {
		case <-r.Context().Done():
			return
		case ev, ok := <-events:
			if !ok {
				return
			}
			if !send("event", ev) {
				return
			}
		case <-metricsTicker.C:
			if !send("metrics", s.config.Hub.Metrics()) {
				return
			}
		case <-keepAlive.C:
			if _, err := fmt.Fprint(w, ": ping\n\n"); err != nil {
				return
			}
			flusher.Flush()
		}
	}
}

type rulesRequest struct {
	Raw   string `json:"raw"`
	Rules []Rule `json:"rules"`
}

type rulesResponse struct {
	Path  string `json:"path"`
	Raw   string `json:"raw"`
	Rules []Rule `json:"rules"`
}

// resolveRaw turns a request into rule file content.
func (s *Server) resolveRaw(req rulesRequest) (string, error) {
	if req.Rules != nil {
		return s.config.Rules.Marshal(req.Rules)
	}
	return req.Raw, nil
}

// GET/PUT /api/v1/rules
func (s *Server) handleRules(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodGet, http.MethodPut) {
		return
	}
	if s.config.Rules == nil {
		writeError(w, http.StatusNotImplemented, "rule management is unavailable")
		return
	}
	if r.Method == http.MethodGet {
		raw, rules, err := s.config.Rules.Load()
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		writeJSON(w, http.StatusOK, rulesResponse{Path: s.config.Rules.Path(), Raw: raw, Rules: rules})
		return
	}
	var req rulesRequest
	if !decodeBody(w, r, &req) {
		return
	}
	raw, err := s.resolveRaw(req)
	if err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	rules, err := s.config.Rules.Apply(raw)
	if err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	s.config.Logf("ruleset updated from web UI (%d rules)", len(rules))
	writeJSON(w, http.StatusOK, rulesResponse{Path: s.config.Rules.Path(), Raw: raw, Rules: rules})
}

// POST /api/v1/rules/validate
func (s *Server) handleRulesValidate(w http.ResponseWriter, r *http.Request) {
	if !methodAllowed(w, r, http.MethodPost) {
		return
	}
	if s.config.Rules == nil {
		writeError(w, http.StatusNotImplemented, "rule management is unavailable")
		return
	}
	var req rulesRequest
	if !decodeBody(w, r, &req) {
		return
	}
	raw, err := s.resolveRaw(req)
	if err != nil {
		writeJSON(w, http.StatusOK, map[string]interface{}{"valid": false, "error": err.Error()})
		return
	}
	rules, err := s.config.Rules.Validate(raw)
	if err != nil {
		writeJSON(w, http.StatusOK, map[string]interface{}{
			"valid": false,
			"error": err.Error(),
			"raw":   raw,
		})
		return
	}
	writeJSON(w, http.StatusOK, map[string]interface{}{
		"valid": true,
		"rules": rules,
		"raw":   raw,
	})
}